The present invention relates to sheet feeders, and more particularly to methods and systems for feeding film sheets from a stack of film sheets in which multisheet feeding is avoided.
Sheet feeders desirably provide individual sheets one at a time from a stack of sheets into a sheet path that conveys the sheets to an operating stage, such as an imaging device. The term "sheet" as used herein refers to a relatively thin, flat, and generally rectangular flexible piece, including without limitation, photosensitive material (e.g., photographic film, X-ray film), paper, transparencies, foil, and the like.
The problems with sheet feeders are well known, and multisheet and misaligned sheet feeding are among the more common and particularly troublesome problems. These problems are even more troublesome when the sheets are expensive, and when multisheet and misaligned feeds waste sheets that cannot be reused. For example, the sheets may be photosensitive material that may be exposed after removal from the sheet feeder. If the sheets cannot be recovered and returned to the stack of sheets without inadvertent exposure, they will be rendered unusable.
The sheet feeder art is replete with attempts to solve the multisheet and/or misaligned sheet feed problems. However, these attempts have focused on rapidly feeding inexpensive sheets (such as paper) and have misfeed rates that would not be acceptable for more expensive sheets, such as X-ray film. Further, the prior art attempts do not attempt to recover a misfed sheet and return it to the stack of sheets once it has been removed from stack of sheets.
The complexity of the multisheet feed problem is increased when there is a relatively high coefficient of friction between sheets. That is, it is more difficult to separate the sheets when they do not slide easily across the top of a stack of the sheets. This problem is particularly acute with photosensitive materials that are likely to have multiple coatings on both sides of the sheet.
Accordingly, it is an object of the present invention to provide a novel sheet feeder and method with reasonable misfeed and sheet recovery rates that obviates the problems of the prior art.
It is another object of the present invention to provide a novel sheet feeder and method in which a feed roller provides sheets to a pair of sheet separation rollers that frictionally urge a sheet therebetween along the sheet path.
It is yet another object of the present invention to provide a novel sheet feeder and method in which a pair of sheet separation rollers for frictionally urging a sheet therebetween along the sheet path each have spaced annular sheet contact surfaces that are interleaved with spaces between the annular sheet contact surfaces on the other roller so that a sheet therebetween is undulated to reduce sheet to sheet static friction.
It is still another object of the present invention to provide a novel sheet feeder and method in which a pair of sheet separation rollers for frictionally urging a sheet therebetween along the sheet path each have annular sheet contact surfaces that are spaced from the sheet contact surfaces on the other roller by a distance related to the thickness of a sheet between the rollers.
It is a further object of the present invention to provide a novel sheet feeder and method in which a pair of sheet separation rollers rotating in the same direction to frictionally urge a sheet therebetween along the sheet path include interleaved sheet contact surfaces wherein one of the rollers provides a coefficient of friction with a sheet that is more than a sheet to sheet coefficient of friction and that is less than a coefficient of friction between contact surfaces on the other roller and a sheet between the rollers.
It is yet a further object of the present invention to provide a novel sheet feeder and method in which a pair of sheet separation rollers have interleaved sheet contact surfaces that are O-rings of silicone on one roller and O-rings of buna-N on the other roller.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the preferred embodiments.